JAVA

How authentication manager works in spring security

Once a user sends a request it  reaches the right authentication filter based on the 
authentication mechanism used.
Now it extract the given credentials from the request and then using the supplied 
values UsernamePasswordAuthenticationToken is  created( the authentication object).
Then  it calls ‘authenticate’ method of the Authentication Manager.
The request then passes to Authentication Provider and the Authentication Provider 
contains an implementation of UserDetailsService.
Spring loads the user information in UserDetailsService  by calling loadbyuserName 
and compares the username/password combination with the credentials supplied at login.